The present invention relates to control of a system machine or process. More particularly, the present invention relates to ascertaining control parameters for a controller to tune a system and achieve acceptable closed-loop control.
Control systems are used in a wide variety of fields, such as industrial processes, environmental systems, electronic systems, mechanical systems, and any other system where system output variables representing measurements and user specified desired outputs are processed to generate signals that control devices which change the system. For example, vibration systems, which are well known, apply loads and/or motions to test specimens. Vibration systems are widely used for performance evaluation, durability tests, and various other purposes, as they are highly effective in the development of products. For instance, it is quite common in the development of automobiles, motorcycles, or the like, to subject the vehicle or a sub-structure thereof to a laboratory environment that simulates operating conditions such as a road or test track.
Physical simulation in the laboratory involves a well-known method of data acquisition and analysis in order to develop drive signals that can be applied to the vibration system to reproduce the operating environment. This method includes instrumenting the vehicle with transducers “remote” to the physical inputs of the operating environment. Common remote transducers include, but are not limited to, strain gauges, accelerometers, and displacement sensors, which implicitly define the operating environment of interest. The vehicle is then driven in the operating environment, while remote transducer responses (internal loads and/or motions) are recorded. During simulation with the vehicle mounted to the vibration system, actuators of the vibration system are driven so as to reproduce the recorded remote transducer responses on the vehicle in the laboratory.
However, before simulation testing can occur, the control system must be tuned. Tuning is the process of setting the controller's internal logic, circuitry and/or variables so that the controller's output signals cause the desired effect given the controller's feedbacks.
Generally, the overall system can be organized or defined as having two principle components, i.e., the “controller” and the “plant”. Operating in closed-loop control, the controller receives inputs or otherwise has stored information pertaining to desired operation of the plant. The controller provides actuation signals to the plant and receives therefrom feedback signals, which can include the remote sensors as discussed above pertaining to the desired response of the plant, and/or intermediate feedback signals deemed necessary to achieve the desired response of the plant. The plant comprises all components that are not part of the controller. Using the vibration system discussed above by way of example, the plant or physical system would include the servo valves, which receive the actuation signals from the controller that in turn are used to operate actuators to impart forces or motions upon the test specimen. The plant would also include any necessary linkages between the actuators and the test specimen as well as test specimen itself and sensors (intermediate and/or remote) used to provide feedback signals back to the controller.
The commissioning of control systems is commonly accomplished by constructing a controller of suitable architecture, connecting it to the plant that is to be controlled, exciting the system while adjusting the control parameters (tune the system) until acceptable closed-loop control is achieved. The tuning process typically requires a significant skill level and is often quite tedious in the case of Single Input Single Output (SISO) systems, and can be overwhelming in the case of Multiple Input Multiple Output (MIMO) systems with a high degree of cross-coupling.
Accordingly, there is a continuing need for an improved method of tuning control systems. A method or system that is easy to use and requires minimal actual plant operation would be very beneficial.